1. Field of the Invention
This invention relates to improvements in instruments for performing near infrared quantitative analysis of organic constituents, such as fat/oil in living bodies as well as in other materials.
2. Prior Art
Two types of near infrared quantitative analysis instruments are known and commercially available. The first type analyzes near-IR energy reflected off the surface of a sample to provide quantitative data on the organic constituents that are present such as protein, oil, and moisture. These type instruments require the sample surface to be very consistent thereby necessitating that the sample be ground into a fine powder with consistent particle size. An example of this type of reflectance instrument is described by James H. Ansow (et al) in U.S. Pat. No. 3,776,642 "Grain Analysis Computer." For a general introduction to near infrared quantitative analysis, see the paper presented by Robert D. Rosenthal to the 1977 annual meeting of American Association of Cereal Chemists entitled "An Introduction to Near Infrared Quantitative Analysis."
A second type of near infrared quantitative instrument analyzes the energy transmitted through a finite thickness of sample (e.g., 2 cm) to provide quantitative data on the amounts of organic constituents present. An example of an instrument of this type is described in U.S. Pat. No. 4,286,327 granted Aug. 25, 1981 to Robert D. Rosenthal and Scott Rosenthal, entitled "Apparatus for Near Infrared Quantitative Analysis" and assigned to the assignee of this invention. This type of transmission measurement approach avoids the requirement that samples be ground into a uniform particle size powder (as in the previous described reflectance measurement approach). However, the transmission approach requires that access to the sample be available on two opposite surfaces; the surface where near infrared energy enters the sample, and the opposite surface where energy exits from the sample.
In certain applications, neither the reflectance measurement need for grinding the sample into a uniform powder, nor the transmission need for a two-sided measurement, can be accomplished. One example of this type of difficult application is the desire to measure the amount of oil in sunflower seeds. Sunflower seeds are highly opaque and thus extremely difficult to measure using transmission technique. It is also extremely difficult to measure reflectance using sunflower seeds because their high oil content, coupled with their tough hull (i.e., shell), precludes grinding them into a fine powder with uniform particle size.
Another example of a difficult application is the desire to measure the amount of fat in humans and in animals.
Fat testing has many uses, but one of the most promising is in connection with non-destructive body fat testing used for medical purposes. The percentage of body fat is an important piece of medical information, and if inexpensive and accurate body fat testing instruments were available, it is believed that most physicians would have one in their offices. It is also believed that many hospitals, sports teams and individual athletes would also have them. Information as to the percentage of body fat could be quite useful in medical diagnosis, medical treatments and general monitoring of a human body's condition, not unlike the uses of blood pressure measuring instruments.
At present there are a number of different ways of measuring human body fat. Obviously, when testing on humans, a non-destructive and non-invasive test or procedure is highly desirable. The most accurate (but also the most frightening) test is a bouyancy test. In such tests a human is weighed out of water and then is weighed in water. However, to be weighed in water all air must be out of the subject's lungs. Obviously such tests require at the very minimum a pool of water and underwater scales, something not available in every physician's office. It is also quite frightening to the test subject who thinks he may drown.
The most common presently known way of measuring body fat is to caliper a pinch of body fat at four separate places on the body, add the total measurement in millimeters and divide by two to get a percentage of body fat. Although this is the most common method in use, it is probably the least accurate. While it is simple and all that is required is a pair of calipers and the ability to add and divide, it is not particularly speedy and its most serious drawback is the lack of accuracy.
Another means of measuring the percentage of body fat is to inject deuterium oxide (D.sub.2 O), then draw blood one hour later and analyze the blood. This method also has its disadvantages in that most people do not like to be injected with anything and this method is not widely used.
The United States Department of Agriculture is interested in the determination of body fat and has experimented in connection with the use of near infrared radiation technology utilizing an optical interactive system with fiber optic tubes. This U.S.D.A. method of testing currently shows the most promise of all of the known approaches to body fat testing.
The U.S.D.A. testing procedure utilizes near infrared radiation and an optical interactance principle in which instead of utilizing reflectance, transmission or a combination of reflectance and transmission, a source of light is directed into the body fat mass by means of a plurality of optical fibers arranged in a circular pattern and a detector is positioned at the end of a second fiber optic bundle located in the center of the illumination tube with an opaque mask separating the illuminating fiber optic tube from the detecting fiber optic bundle on the surface of the body fat between them. The interactance of the light with the body fat is detected by the detector and utilized for a reading.
While the U.S.D.A. instrument shows promise, especially from the standpoint of providing accurate and versatile measurements, it is expensive to manufacture utilizing expensive fiber optics. An article describing the U.S.D.A. development is currently being prepared for publication.